This invention relates in general to land vehicles and more particularly, to personal mobility vehicles. Most particularly, the invention relates to wheelchairs having adjustable backrests.
A wheelchair typically consists of a wheelchair frame that supports a seating structure, a backrest, and a plurality of wheels. A wheelchair backrest is commonly designed so that it can be positioned at various angles with respect to the seat platform. The seat platform is also typically adjustable to be positioned at various angles with respect to horizontal. This adjustment allows the wheelchair to accommodate individuals with specific seating and positioning needs, where the back angle and seat angle are critical for comfort, correct posture, performance, and other therapeutic requirements. Wheelchairs often incorporate folding backrests that allow the overall size of the wheelchair frame to be reduced in order to store or transport the unoccupied wheelchair. These wheelchairs typically have backrests that fold down against the seat platform to reduce the overall size of the frame.
Historically wheelchairs have employed the use of machined steel or aluminum plates to join the seat frame to the back frame. A latching mechanism is typically included such that the backrest can disengage and pivot to fold. The seat frame and back frame are usually constructed from steel or aluminum tubing. The plates are bolted to the sides of this tubing, and allow a limited range of angle adjustment between the seat and the backrest by providing a plurality of holes through which the backrest or seat can be bolted. One disadvantage of such a system is that the plates extend some distance along the seat tubes, occupying valuable real estate on the seat frame that is desirable for attaching other components, such as wheel mounting hardware. Another disadvantage is that the plates place undue stress on the backrest and seat tubes, and require that the tubing be thicker walled in order to withstand the stress. This results in a heavier wheelchair. These backrest systems often require that the wheelchair be unoccupied when adjustment is made to the back angle. This is inconvenient for the therapist and patient, where it is easier to properly fit a chair while the patient remains seated.
What is needed is a strong, lightweight means for attaching a wheelchair backrest that allows adjustability over a large range of backrest angles, provides a fine resolution of available angles, can be adjusted while the patient remains seated for correct fitting, and allows the backrest to be folded down for compact storage.